The invention relates to medical instrumentation, in particular to diagnostic measuring devices, and can be applied, for example, for high-accuracy vision correction.
Methods are known for measuring the wave aberrations of the optical system of the human eye as a function of spatial pupil coordinates. Said methods use probing the eye with a thin laser beam, its backscattering by the retina, detection of the component exiting from the eye by means of photosensitive devices, and measurement of the wave front tilt in different pupil points with known coordinates. These data are used for the wave front approximation and calculation of the wave aberration of the eye as wave front deformations.
Some methods use measurement of the wave front structure at the exit of the eye simultaneously in time by means of partitioning this structure into subapertures (D. R. Williams, et al. Rapid, automatic measurement of the eye's wave aberrations. U.S. Pat. No. 6,199,986. Int. Cl. A61B 3/10, 13.03.2001). Subapertures are formed using a matrix of coaxial lenses and a matrix of position sensing photodetectors installed in their foci. The wave front is reconstructed from the measured set of tilts simultaneously in all subapertures.
Ray tracing method for measuring the wave front and refraction aberrations successively in time (V. V. Molebny, et al. Device for measuring refraction aberrations of the eye. (Ukrainian Patent Application No. 98105286, now Patent No. 46833, Int. Cl. A61B 3/00, A61B 3/10, A61B 3/14, filed Oct. 7, 1998), is also known. According to this method, the eye is probed by a thin laser beam (its cross-section at the eye entrance is 0.2-0.3 mm), shifted in parallel to itself over the entrance aperture of the eye successively in time, the coordinates of the points on the retina, to which the laser beam is projected, are measured at each probing. Said data obtained in a discrete set of points of the eye aperture are used to calculate the wave front tilt in these points and then approximate the entire wave front surface.
Both of the above mentioned methods use the approximation of the wave front using a series of Zernike polynomials. The use of said series results in some restrictions, which lead to non-uniform spatial resolution when describing the refraction non-homogeneity over the eye aperture. Thus, in the central zone, which is the most significant for the acuity of vision, spatial resolution is lower than in the peripheral zone if describing the refraction non-homogeneity by means of Zernike polynomials.
To obtain a higher spatial resolution in the center, the number of polynomials must be increased, therefore, measurements in the larger number of aperture points are required, not only in the center but also at the periphery, making the procedure of measurement more complicated: radiation exposure of the eye is increased, calculation process becomes significantly longer and more complicated (the number of equations increases to a few hundreds).
Both above mentioned methods are equivalent from the point of view of wave front approximation using the series of Zernike polynomials. Each method can be regarded as a prototype. Let us take the ray tracing principle for a prototype.